The invention relates to positive displacement reciprocating compressors of the type having at least two compression stages arranged in series.
For some time now the prior art has embraced hydraulically-driven positive compressors of the reciprocating type, generally consisting of three coaxial bulkheads between which two coaxial cylinder barrels are located.
Each barrel accommodates a relative piston which strokes, fluid-tight, connected to the remaining piston by a rod; two chambers are thus enclosed by the pistons, the cylinder barrels and the central bulkhead, into which hydraulic oil is pumped, thereby creating a double-acting fluid power cylinder. The remaining two enclosures at either end, created by the pistons, the barrels and the outer bulkheads, or end caps, provide compression chambers.
Such compressors are utilized for the purpose of raising gas from a given initial pressure, which may be atmospheric, to ultra high pressure.
Gases are compressible; it follows therefore that an increase in pressure signifies reduction in volume, to a degree dependent on the final pressure that must be reached. This final pressure is arrived at gradually, for obvious reasons of bulk, employing either multi-stage compressors or a string of single compressors.
Problems with prior art compressors are encountered mainly at low pressure; in the first stage in particular, large bores are required in order to produce powerful suction as a result of the running speed, which is relatively low, especially when compared with mechanically-driven compressors.
Conversely, force required to compress the gas is significantly small, and with hydraulic oil constantly entering at the same high pressure, the need arises for a drastic reduction in the surface area of the piston on which this oil impinges. Such a requirement is met currently by enlarging the diameter of the piston rod; this signifies a considerable increase of the mass set in motion, however.
An increase of the mass set in motion not only renders the compressor singularly heavy, but also limits maximum velocity of the reciprocating components, limiting performance as a result.
Another problem encountered with prior art compressors is that, in the light of the above circumstances, it becomes necessary to employ one compressor of some considerable size for the initial stage, and at least one further compressor of more compact dimensions for successive stages.
The object of the invention is to eliminate the drawbacks described above.